Nacre from the shells of bivalves, also known as mother-of-pearl, is about three thousand times tougher than the fragile ceramic it is made of (aragonite, 95% by volume). This improvement in toughness is the result of an extremely well designed structure arranged over several, distinct length scales (hierarchical structure). Microscopic aragonite tablets are arranged as overlapping layers similar to a three dimensional brick wall, and having a nanometers thick layer of soft organic material acting as a mortar (see FIGS. 1A and 1B). Ceramic materials, including aragonite, have many attractive engineering qualities such as stiffness, hardness, wear resistance, and resistance to high temperatures. The main obstacle to a wider use of ceramics in engineering applications is their brittleness: they fail at very small deformations and in a catastrophic fashion, and they are fragile in tension.
Several attempts at mimicking nacre have been made, but to this day none can reach the degree of toughness improvement of nacre (see Clegg, W. J., et al. (1990) Nature 347: 455-457; Tang, Z. Y., et al. (2003) Abst. Papers Am. Chem. Soc. 226; 413-418; Sellinger, A. et al. (1998) Nature 394: 256-260 (1998); Dabbs, D. M. and Aksay, I. A. (2000) Ann. Rev. Phys. Chem. 51: 601-622; Mayer, G. (2006) Mat. Sci. Eng. C—Biomimetics Supramol. Syst. 26: 1261-1268; and Deville, S., et al. (2006) Science 311: 515-518).
The prior art demonstrates that there is a current and long-felt need for an improved composite material having properties similar to natural nacre or mother-of-pearl. Such composites can have uses in aeronautics, defensive material, orthopedics, and MEMS (micro-electro-mechanical systems).